Over the past 30 years, there has been an almost religious commitment to the privatisation of water on the part of the World Bank, international donors, and many UN agencies. Millions are spent each year by these institutions on pro-privatisation conferences, workshops and publications, not to mention loans and grants to make it happen.

It is refreshing, therefore, to know that there is at least one UN institution committed to improving public water provision. Founded by UN-Habitat in 2009, the Global Water Operators' Partnerships Alliance (Gwopa) is a platform for bringing together public water operators from around the world.

The agency's mandate is to build public sector capacity, while at the same time creating "solidarity, learning, friendship, cultural experience, career development and integrity" across municipalities and countries. Many innovative north-south and south-south linkages have emerged, and public water is better off because of it.

Participation in Gwopa is also open to organised labour, NGOs, community groups and academics, as evidenced at the agency's second congress, which took place last month in Barcelona.

This is a small, pro-public ship on a rough, pro-private ocean, but it is an important institution that has the potential to create meaningful networks, conduct critical research, and build links between governments, unions and communities.

And no wonder. Research has shown that public water can outperform private companies even on their own narrow financial terms, not to mention doing a better job with equity, participation and public education. No public service will ever be perfect, but there is growing understanding of what makes public water work, how we might make it better, and the variety of ways of getting there.

As a UN institution, Gwopa is uniquely placed to advance this agenda and help break down the geopolitical barriers that can make it difficult for public utilities to work with each other across borders. For this reason alone, it is an institution worth fighting for.

Gwopa has its internal tensions, however. From the outset, the association has been open to private water companies, represented by Aquafed, a federation of the largest water multinationals in the world. Gérard Payen, former CEO of Suez's water division, represents this group at Gwopa, and was recently reappointed to the steering committee for another four years.

Gwopa documentation also talks about the need for "commercially viable" water services and tends to use the same narrow financial performance indicators as private companies, encouraging market-based operating principles.

The agencies that fund Gwopa appear to reinforce these trends, with one senior aid representative at the Barcelona congress suggesting she "does not care if the water providers [involved in the alliance] are public or private, as long as they get the job done".

There is also creeping commercialisation evident in some of the public water utilities working within Gwopa, many of which think and operate like private companies (for example by seeking private contracts outside their own country). This serves to blur the lines between public and private.

These are not insignificant strains. Gwopa must decide what it means by "public water" and how it wants to evaluate successful public performance. It must be open to critical self-reflection and offer water providers something other than run-of-the-mill rhetoric about the need for more market-oriented management.

Public water is different to private water, and Gwopa must figure out where it stands on this debate if it is to make an innovative contribution to water policy and practice.

Ultimately, the vast majority of the world's water systems remain in public hands, and many more are being put back into government hands. What we really need is 20 Gwopas to engage with this reality; for now, one effective one will do.

• David McDonald is co-director of the municipal services project, and professor of global development studies at Queen's University in Canada.